1. Field of the Invention
The present invention relates to fiber optic assemblies and in particular, to a system and instrument for verifying the routing and measuring the insertion losses of multiple fiber optic assemblies.
2. Description of the Related Art
The availability and proliferation of multiple fiber optical connectors has increased the complexity of cable assemblies necessary for routing the signals generated by transmission equipment into multiplexers and other local equipment. Until recently, single optical fiber cables were used to direct the signals between relevant points. In many cases this involved hundreds of cable assemblies which occupied a fair amount of space and were difficult to organize.
To solve this problem, special cable arrangements like shuffles and flexible fiber circuits were introduced. Essentially, these arrangements consist of a collection of multiple fiber connectors, normally 8, 12 or more fiber MT or similar type fiber optic connectors, or a combination of multiple fiber and single fiber connectors, organized as input and output connectors. Fibers are then routed from one position in an input connector to another position in an output connector according to the specified routing requirements. By partially organizing the fibers in a ribbon fashion a very compact arrangement can be obtained.
FIG. 1 shows a shuffle type cable assembly. In particular, the input side connectors 101, the output side connectors 104 and the optical fibers 102 are shown. FIG. 2 shows a flexible circuit type cable assembly. The optical fibers 102 are glued on a flexible substrate 103. Shown also are the input side connectors 101 and the output side connectors 104.
Normally the specifications of these circuits involve a table showing the start and end of each fiber, from one of the many positions in a particular multiple fiber connector to one of the many positions in another particular multiple fiber connector. It is important to verify the correctness of the routing. Sometimes it is also necessary to determine the insertion loss (attenuation) introduced into the overall system by the cable assembly. This is important because of optical power budgeting considerations.
In any fiber optic interconnection, some loss occurs. Insertion loss for a connector or splice is the difference in power that is seen by the insertion of the device into the system. Insertion loss (or attenuation) is defined as the difference between the optical power launched into an interconnection cable and the optical power measured at the opposite end, or mathematically as follows:Insertion Loss=10×log (P1/P0) dB
Wherein P0 is the power of the optical signal launched into a cable, and
P1 is the power of the optical signal as it passes out of the cable.
At present, there are two main methods to verify that routing is correct and to measure insertion losses. The first method consists of using a set of a limited number of light sources and detectors (usually 12 of each or less). Launching and receiving cables connected on one side to these light sources and detectors on the other side, respectively, are terminated with the required connector and then mated successively with the connectors in the shuffle or flexible circuit.
Only one multiple connector from the launching cable is mated with the connector in the shuffle or flexible circuit arrangement at one time. Since fibers in the arrangement could be routed arbitrarily from input to output connectors with fibers in one input connector being normally routed to one or more different output connectors, this implies that the mating of the cables has to be repeated several times for the same connectors, both in the input and output sides in order to verify the routing or measure the insertion losses. This not only increases the time and labor consuming nature of the measurement process, but the multiple operations of connecting and disconnecting might damage the fiber termination in the launching cables or the cable assembly arrangement itself. Moreover, determining the base power (P0 in the insertion loss formula) increases the complexity of the measurement.
The second method involves the use of optical switches. In this case, one light source is directed to each input fiber successively by mechanically or otherwise switching the light. Similarly, the light leaving each output fiber is switched to a single detector. The drawback of this last method is that optical switches for large numbers of positions are normally mechanically driven and consequently slow and bulky. Precision requirements also tend to make them expensive.
Accordingly, there is an unfilled need for a cost-effective system and instrument for quickly, easily and efficiently verifying the routing and measuring the insertion losses of multiple fiber optic assemblies. The present invention employs lasers and detectors that are currently manufactured in large quantities and relatively inexpensively so as to bypass the drawbacks of the two conventional methods mentioned above.